NASA astronauts ventured back outside the International Space Station on Wednesday for more cable work and a lube job.

It was the second spacewalk in five days for Butch Wilmore and Terry Virts. In all, three spacewalks are planned in just over a week to prepare the orbiting lab for future American crew capsules.

"Take it nice and slow," Mission Control advised the two men as they got started a little early.

Virts was supposed to spend half of Wednesday's spacewalk lubricating latches and brackets on the end of the station's giant robot arm. He and Wilmore also had to install more power and data cables, for a two-day total of 364 feet. They unreeled the first eight cables Saturday; only two remained Wednesday.

By the end of their third spacewalk scheduled for Sunday, they will have routed 764 feet of cable on the station's exterior. NASA considers it the most complicated cable job ever at the 260-mile-high, 16-year-old outpost.

The extensive rewiring is needed in advance of this year's arrival of a pair of docking ports, designed to accommodate commercial crew capsules still in development. NASA expects the first port to arrive in June and the second in December.

SpaceX and Boeing are designing new capsules that should start ferrying station astronauts from Cape Canaveral in 2017. Manned flights have been on hold at the cape since NASA's shuttles retired in 2011. SpaceX already is launching station cargo.

NASA has contracted out space station deliveries so it can concentrate on getting astronauts farther afield in the decades ahead, namely to Mars.